A report by the US Congress on Wednesday faulted former secretary of state Hillary Clinton over the deadly attack on the US mission in Benghazi, saying she rejected requests for greater security.

The report by the Republican chairmen of five committees in the House of Representatives said that the Democratic administration failed to react to warnings of security risks in Libya after the fall of dictator Moamer Kadhafi.

The report said that the State Department knew that the US mission in the eastern Libyan city was "vulnerable and unable to withstand an attack" but "continued to systematically withdraw security personnel."

Clinton signed a cable in April 2012 that turned down requests by US diplomats for greater security due to a lack of resources, the report said.

"The committees' review shows that the leadership failure in relation to security and policy in Benghazi extended to the highest levels of the State Department, including Secretary Clinton," it added.

The assessment contradicts Clinton's statement before Congress in January, when she stood by a review by a State Department board that said that cables on security came only to the attention of lower-ranking officials.

Clinton -- seen as a frontrunner for the Democratic nomination for president in 2016 if she decides to run -- said that 1.43 million cables are addressed each month to the secretary of state.

But Clinton has also accepted responsibility for the consequences of the attack, which took place last year on September 11 and killed four Americans, including ambassador Chris Stevens.

The report said that Stevens sent an email in June saying that the US mission "would feel much safer" with additional security due to upcoming elections.

The five Republican chairmen signed a letter that asked President Barack Obama to release publicly the April 2012 cable and to provide to Congress additional emails related to controversial public statements on the attack.

A spokesman for Clinton did not immediately return a request for comment. The State Department rejected the findings of the report.

The findings "are not consistent with what we believe in terms of our transparency and the work that we've done, so we don't agree with their conclusions," State Department spokesman Patrick Ventrell told reporters.

Ventrell said that the State Department provided 20 briefings to Congress, cooperated with eight hearings and provided 25,000 pages of documentation on the Benghazi attack.

"We're very determined to continue to cooperate, and we've been clear that we've had unprecedented cooperation to date," he said.